1. Field of the Invention
The present teachings relate to an antenna for a towed submersible device. More particularly, the present teachings relate to an apparatus and method for automatically raising and lowering an antenna from the body of a towed communications buoy.
2. Description of the Prior Art
As known in the art, communication buoys can be towed behind submarines by a deploying and retrieving cable. During operation and upon release from a submarine, known communication buoys are designed to rise to the surface of the sea. At the sea surface, the communication buoys deploy equipment, such as, an antenna that permits the submarine to carry-on radio communications with other, sea, land, and air-based communication systems, such as satellites.
When not in use, the communication buoys are retrieved and stowed in uniformly-shaped containers formed in the superstructure or pressure-hull of a submarine. Storing communications buoys within the superstructure or pressure-hull of a submarine protects the buoys and provides maximum submarine maneuverability. However, any portion of the deployed antenna that extends beyond the main body of the communications buoy must be retracted to permit efficient storage.
In the past, complicated electro-mechanical devices have been used to articulate the masts and antennas of communication buoys. For example, electric motors and pumps have been used for turning a jacking screw or to move a hydraulic ram to articulate an antenna. Such devices are large and heavy; thereby, requiring additional buoyancy and additional resources, such as electricity, to operate. In addition, these devices are difficult to seal or make pressure-tolerant to prevent fouling by organic and inorganic materials. Moreover, because communication buoys are expendable, the added cost of an electro-mechanical articulation device reduces their cost-effectiveness.
Furthermore, radio-frequency communications antennas when used with towed communication buoys suffer a degradation of performance at or near the surface of the sea. This degradation can be attributed to the fact that a seawater-atmospheric boundary presents an imperfect environment for operating antennas. The seawater-atmospheric boundary can be characterized as a non-uniform, a non-perfect conducting, and a non-free space ground plane. Moreover, seawater washing onto the antenna of a communications buoy can contribute to the degradation of antenna performance.
The imperfect seawater-atmospheric boundary can affect the antenna's electrical characteristics by dynamically changing the antenna's instantaneous electrical parameters resulting in a time-varying gain and pattern. Washing over seawater prevents the antenna from transmitting or receiving RF energy and can result in the receipt of system self-noise or erroneous information.
As a result of that which was described above, there exists a need to provide a lightweight, inexpensive, compact and simple apparatus for automatically raising and lowering an antenna from the body of a towed communications buoy. There also exists a need to provide such an apparatus that can reduce or eliminate the degradation of performance by raising the antenna the greatest extent possible from the seawater-atmospheric boundary. There still further exists a need for such an apparatus that is foul-resistant and sea-pressure tolerant.